There are other things not covered by PEAR Coding Standards which
are mostly subject of personal preference and not directly related
to readability of the code. Things like "single quotes vs double
quotes" are features of PHP itself to make programming easier and
there are no reasons not use one way in preference to another. Such
best practices are left solely on developer to decide. The only
recommendation could be made to keep consistency within package
and respect personal style of other developers.